We describe the use and characterization of a multilayer film, prepared via layer-by-layer deposition of cationic para-rosaniline acetate dye (i.e., PR) and the vanadium-containing Keggintype polyoxometalate anion, [PMo 11 VO 40 ] 5 (i.e., PVMo 11 ), on indium tin oxide (ITO) as an electrode for determination of chlorate. A linear cyclic voltammetry (CV) current response was observed for the 0 M [ClO 3 ] 1000 M range with a detection limit of ~220 M ClO 3 (S/N > 3) in a pH = 2.5 solution of 100 mM sodium acetate. Electrode response was insensitive to interference by oxygen and nitrogen-based explosives like TNT, a prerequisite for use in the field. A Taguchi L16 array was used to investigate the performance of the electrode as functions of number of PVMo 11 /PR bilayers (L; 3-6 bilayers), solution pH (H; pH ~1.32 -2.85), solution [ClO 3 ] (C; 250 -1000 M), CV scan rate (S; 50-200 mVs 1 ), and film age (A; 1-8 weeks). Maximum current response was obtained for a 1 week old 5 bilayer film immersed in a pH 2.85 0.10 M NaCl (aq) solution containing 1000 M ClO 3 . However, current response fell as films aged, requiring aging of films for approximately 8 weeks prior to use to obtain reproducible analyses. A two-level full factorial design using films aged 8 weeks identified the variables S, L, H, and C and variable interactions LS and HS as statistically significant contributors to the film current response and provided a model describing film performance.